1. Field of the Invention
The present invention relates to an MgO protective layer material for use in a front substrate of a plasma display panel and a method of fabricating the same, and more particularly, to a method forming a protective layer for a plasma display panel by using an MgO pellet simultaneously doped with a first doping material of BeO and/or CaO among alkali earth metal 2 group and a second material selected from the group consisting of Sc2O3, Sb2O3, Er2O3, Mo2O3, and Al2O3, through a thin film forming process, such as electron-beam evaporation, ion plating, or sputtering, in which the first doping material and the second doping material are respectively doped the range of 50 ppm to 8000 ppm.
2. Description of the Prior Art
A PDP is a flat display panel, and is usually employed in wide display apparatuses of more than 40 inches because of their good image quality and thin and light features. The PDP includes a plurality of barrier ribs formed on a front substrate, a plurality of address electrodes formed on the rear substrate, and a plurality of sustain electrodes formed on a front substrate, in which pixels are formed at cross areas of the address electrodes and the address electrodes to form an image.
In FIG. 1 there is schematically shown the structure of such a PDP. A front substrate 10 made of a glass or metal substrate is coated by a transparent dielectric layer 20, and an address electrode 50 is formed on the rear substrate 80 or the rear dielectric layer 90. A stripe barrier rib 60 is interposed between the address electrodes 50, and a spatial surface defined by the barrier ribs is coated by a phosphor to form a sub-pixel. A plurality of sustain electrodes and scan electrodes are formed on a front substrate 10 made of glass. An upper dielectric layer 20 is formed to cover the sustain electrode 40 and the scan electrode, and an MgO protective layer 30 covers the upper dielectric layer 20. When the front substrate 10 is coupled to the rear substrate 80, a plurality of pixel spaces isolated by the barrier ribs 60 are formed between the substrates. The isolated spaces are filled with a discharge gas, such as a rare gas of Ne and Xe or Ne, He, and Xe, and are sealed at a certain pressure.
If a driving voltage is applied to the sustain electrode 40 and the address electrode 50, plasma is produced in the spaces due to glow discharge. If a sustain voltage is applied to the sustain electrode and the scan electrode, a glow discharge is produced between the sustain electrodes in the discharge cell, in which a wall voltage is produced. In this instance, the phosphor coated on the sidewalls and bottom surface of the discharge cell is exited by vacuum ultraviolet rays produced from the plasma to generate red, green and blue visible rays.
The MgO protective layer induces secondary electron emission and exoelectron emission in the glow discharge, thereby attenuating the discharge voltage and improving a discharge delay. Therefore, the MgO protective layer is used as an electron emission layer from an early stage the PDP's development. In order to reduce the consumption power of the PDP, however, secondary electron emission coefficient should be further improved to attenuate a discharge starting voltage. In addition, in order to reduce costs of components to be required for single scan drive, it should further improve the discharge delay induced by the improved feature of the exoelectron emission.
Several methods of improving the secondary electron emission coefficient by using oxide doping have been proposed. Specifically, the method is to positively adjust an electron emission characteristic of MgO by controlling a defect energy level and concentration of MgO using a doping element. It is known that Auger neutralization leads to the secondary electron emission from an MgO surface, which is shown in FIG. 2. When ions generated through discharge of the PDP reaches the MgO surface, electrons in a 2P electron orbit of oxygen ion of MgO induces neutralization with ions due to tunneling. The energy generated at that time is transferred to the electrons existed in a valance band, thereby emitting the electrons outwardly. It is possible that metastable energy of the discharge gas, photon energy, and an electric field of wall charge supply the energy required for the secondary electron emission, as well as ionization energy of the discharge gas. Consequently, in order to emit the electrons by use of various energy sources to be generated at the PDP discharge, it is necessary to a defect level in the MgO band gap, thereby easily emitting electrons.
The method of improving the electron emission by adding a doping element is disclosed by Japanese Patent Application Nos. 2003-00331163 and 2003-00335271, Korean Patent Application Nos. 2004-0037268, 2004-0108075, and 2005-0061426, and U.S. Patent Application No. 2006-0145614.
Japanese Patent Publication No. 2005-123172 proposes MgO materials using at least one element selected from Si, Ge, C, and Sn, and at least one element selected from fourth, fifth, sixth and seventh group element of the periodic table as a doping element. Each concentration of at least one element selected from Si, Ge, C and Sn ranges from 20 ppm by weight to 8000 ppm by weight, and each concentration of at least one element selected from fourth, fifth, sixth and seventh group elements of the periodic table ranges from 10 ppm by weight to 10000 ppm by weight.
Japanese Patent Publication No. 2005-123173 proposes MgO materials comprising magnesium carbide such as MgC2, Mg2C3, or Mg3C4. A concentration of the magnesium carbide ranges from 50 ppm by weight to 7000 ppm by weight.
Korean Patent Application No. 2005-0061426 provides a protective layer doped with Si. The composite has a characteristic in that a discharge delay is minimized. In this instance, contents of impurities are limited to Ca of up to 50 ppm, Al of up to 250 ppm, Ni of up to 5 ppm, Na of up to 5 ppm, and K of up to 5 ppm.
Korean Patent Application No. 2004-0037268 provides a material of an MgO protective layer using as dopants including Ca, Al, Fe, and Si. These dopants minimize a time of PDP discharge delay due to their interaction with each other. There is disclosed a composite consisting of Ca of 100 to 300 ppm, Al of 60 to 90 ppm, Fe of 60 to 90 ppm, Si of 40 to 100 ppm.
Korean Patent Application No. 2004-0108075 provides an MgO composite consisting of one or more elements selected from the group consisting of Al, Ca, and Si, in addition to at least one selected from the group consisting of rare earth elements. The composite consists of Sc of 50 to 600 ppm per 1 gram of MgO, Ca of 50 to 400 ppm per 1 gram of MgO, Al of 50 to 400 ppm per 1 gram of MgO, and Si of 50 to 400 ppm per 1 gram of MgO. In addition, the composite contains impurities consisting of Mn, Na, K, Cr, Fe, Zn, Bi, Ni, and Zr, in which Mn is up to 50 ppm per a gram of MgO, Na is up to 30 ppm per a gram of MgO, K is up to 30 ppm per a gram of MgO, Cr is up to 10 ppm per a gram of MgO, and Fe is up to 20 ppm per a gram of MgO.
U.S. Patent Application No. 2006-0145614 provides an MgO composite doped with Sc, Ca, and Si. The patent discloses that if a content of Sc ranges from 50 ppm to 2000 ppm, a content of Ca ranges from 100 ppm to 1000 ppm, and a content of Si ranges from 30 ppm to 500 ppm, the discharge delay is remarkably minimized. The use of the doped MgO or the adjustment of atmosphere conditions of MgO deposition improves the characteristic of the MgO layer, thereby improving the discharge efficiency and shortening the time of discharge delay, which remarkably contributes to a performance of the PDP.